1. Field of the Invention
The present invention broadly relates to arthroscopic surgical instruments. More particularly, the invention relates to arthroscopic surgical instruments which are preferably disposable and which include push rods with a failure mechanism for excess force, and end effectors with desired arrangements.
2. State of the Art
The arthroscopy procedure has become a widely practiced surgical procedure. Arthroscopy involves making one or more relatively small incisions in order to examine the interior of a joint with an endoscope and to perform surgical operations on the joint. Typically, the surgical procedure involves inserting a cutter, dissector, or other surgical instrument through at least one incision for purposes of manipulating and/or cutting the bone, meniscus, tissue, and cartilage comprising the joint.
The disposable arthroscopic tools of the prior art are somewhat similar to other endoscopic tools used in endoscopic procedures involving softer tissues and organs. These tools, such as laparoscopy tools, generally include a tube, a push rod which extends through the tube, an actuating means engaging the tube and the push rod for imparting reciprocal axial motion to the push rod, end effector means coupled to the push rod, and a clevis coupled to the tube at its proximal end and to the end effector means at its distal end, wherein axial movement of the push rod effects movement of the end effector means in a plane parallel to the longitudinal axis of the push rod. The end effector means of the art can take any of many forms, such as, e.g., a scissors, a dissector, or a grasper. Additionally, the end effector means can be double acting or single acting.
Since there is a limit as to how strong the tools of the art can be made and still be small enough for use in arthroscopy, there is always the possibility that the tool will break while in use. Indeed, this problem is compounded with disposable tools, typically made from weaker materials than the standard stainless steel of non-disposable tools. While this is a remote possibility in most endoscopic procedures involving soft or relatively soft tissues, when used in arthroscopic procedures involving bone tissue, the possibility that an end effector or distal linkage member will break is increased since additional force must be applied to the end effectors through the actuating means in order to grasp or cut the bone tissue. In such a case, if a portion of the end effector or distal linkage breaks, it may become lodged in the joint and will require additional procedures to remove it.
In the field of endoscopy, U.S. Pat. No. 4,896,678 to Ogawa partially addresses this problem. In Ogawa, means are provided for releasing the transmission of force to the end effectors when the operating force exceeds a predetermined amount. One mechanism used by Ogawa to release the force is a V-shaped notch in the push rod which is intended to fail upon the application of excessive force. The teachings of Ogawa, however, have not been applied to arthroscopic instruments in the past.
Improvements have been made in end effectors for use in arthroscopy. In particular, durable surgical forceps and punch end effectors are disclosed in U.S. Pat. No. 4,712,545 to Honkanen. Honkanen's end effectors comprise a stationary jaw and a movable jaw wherein the movable jaw is attached to the stationary jaw by a first arcuate lug and groove arrangement and to a push rod by a second arcuate lug and groove arrangement. The push rod moves relative to the stationary jaw and engages the movable jaw by the second lug and groove arrangement so that the movable jaw is forced to slide by the first lug and groove arrangement relative to the stationary jaw to open or close. The jaws are configured in different ways to act as a punch or a forceps. This arrangement relieves much of the stress associated with the pivot point on end effectors, but is a relatively complex construction, particularly with regard to the second arcuate lug and groove arrangement.
Other strength enhancing improvements in end effectors are disclosed in U.S. Pat. No. 5,152,780 to Honkanen et al. which describes a stationary jaw having an integral clevis pin and a movable jaw having an arcuate engaging groove coupled to a push rod having a stud. The stationary jaw is generally U-shaped member with a hourglass shaped integral pivot pin. The movable jaw has a slot which seats on the pivot pin. Engagement of the push rod stud with the groove on the movable jaw holds the movable jaw against the pivot pin and rotates the movable jaw about the pivot pin.
Despite the many improvements in arthroscopic instruments in recent years, there are still several disadvantages which need to be overcome. Most arthroscopic end effectors comprise a generally U-shaped stationary member with a movable inner punch member having a serrated surface. A disadvantage of this construction is that force applied to the end effector is distributed over the entire tissue grasped within the U-shaped member. This limits the efficiency of the cutting action of the punch. In addition, the serrated surface sometimes pushes the tissue out of the U-shaped member before it can be cut. Moreover, while certain improvements have been made in frangible links to prevent end effector breakage, some of these links are difficult to manufacture. In addition, while it is known to supply certain endoscopic instruments with a cautery current, arthroscopic instruments have never before been provided with cautery capability.